Modernize GitHub Action and Python versions

[achimnol]

This PR modernizes several GitHub Action versions and let the CI use latest supported Python versions.

• Drop support for obsolete Python versions older than 3.8
• Replace isort and flake8 with Ruff (including formatter and fixers)
• Enable Ruff's Black preview style, and apply the updated code style
• Upgrade mypy to 1.10.0
• Apply the no_implicit_optional tool
• Upgrade pytest and pytest-asyncio with asyncio-mode = true, deprecating the custom event_loop fixture implementation
• Adopt latest GitHub Actions improvements, such as intrinsic pip cache support in setup-python and official token-based codecov-action

Checklist

• [x] I think the code is well written